1. Field of the Invention
This invention relates to alignment apparatus, and more particularly, to an apparatus to adjust a holding means for a semiconductor wafer or other substrate as needed for extremely accurate positioning with respect to a mask used in the fabrication of semiconductor or other devices from the wafer or substrate.
The invention has particular utility in X-ray lithography printing processes wherein the wafer, covered with photosensitive material, and a mask(s) of the circuit to be made, are brought into registration. The wafer is mounted on a movable support plate or stage which is translated in x-y axis directions, in rotation .theta., in mask-wafer gap spacing and in tilting or angular orientations with respect to the mask.
2. Description of the Prior Art
The X-ray lithography system in which the alignment stage of this invention finds general utility is seen in U.S. Pat. Nos. 4,037,969 and 4,326,805 wherein zone patterns are formed on spaced-apart mask and wafer(s) and are used for alignment purposes in the fabrication of integrated circuits. Off-axis illumination of the patterns is provided affording a significant mask-to-wafer alignment capability in the x and y axis, in rotation .theta., and in the gap space between the wafer and mask. The zone plate patterns serve as a basis for adjusting the mask-to-wafer separation. U.S. Pat. No. 3,870,416 describes a wafer alignment device useful in the above prior art systems which comprises a support platform supported by three flexible rods extending to a linking ring. Three additional rods extend from the ring to a stationary table. The support platform is movable in the x, y and .theta. directions to align the wafer without movement in the Z direction. Forces to move the support platform are applied at midpoint between the platform and the lower linking ring by piezoelectric transducers applied to a hollow cylinder extending downwardly from the support platform. The ring is located in a reservoir of viscous fluid to damp vibrations during adjustment and scanning. Other support platforms have been utilized in X-ray lithograph systems but are very large and cumbersome having an envelope size up to 48".times.48".